Implement API response caching with ETags

[Smartdevs17]

Context

API responses need ETag caching.

Current Limitation

No ETag support.

Expected Outcome

• ETag generation
• Conditional request handling
• Cache-Control headers
• Stale-while-revalidate

Acceptance Criteria

• ETag generation from response
• If-None-Match handling
• 304 Not Modified responses
• Cache-Control per endpoint
• Stale-while-revalidate
• Cache bypass for auth
• ETag collision testing

Technical Scope

• backend/services/shared/ - ETag middleware
• backend/services/ - API endpoints
• developer-portal/ - API docs
• docs/ - Caching documentation

[Malcolm-Wander]

@Malcolm-Wander has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hello maintainer,I’d love to work on this issue please,I promise to do a good and swift job..thank you very much

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[ValJnr-dev1]

@ValJnr-dev1 has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hi Maintainer,

I’m a smart contract and full-stack developer and would love to contribute to this issue. I’m an experienced contributor with hands-on expertise in Rust, Soroban, Cairo, and TypeScript.

I’m passionate about building secure, scalable blockchain solutions, with a strong emphasis on writing clean and maintainable code. Based on the scope of this issue, I’m confident I can deliver a complete solution within 24 hours of assignment.

I’d greatly appreciate the opportunity to contribute and help move this forward.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @ValJnr-dev1 to this issue.

[Samaro1]

@Samaro1 has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Gm gm boss, I would love to work on this issue. A satisfactory and efficient PR will be raised. Please assign this to me

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[bulusmalaga]

@bulusmalaga has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hi Maintainer,

I’m a smart contract let me solve this

ℹ️ Repo Maintainers: To accept this application, review their application or assign @bulusmalaga to this issue.

[drips-wave]

Congratulations, @bulusmalaga! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on July 30, 2026.

🧑‍💻 @bulusmalaga: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

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[drips-wave]

This issue has been completed by @bulusmalaga as part of the Stellar Wave Program's 7th Wave 🥳

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